1. Field of the Invention
The present invention relates to electrical fuse devices each comprising a plurality of stages of fuse cores, each fuse core having an electrical fuse element and a switching element, serially connected together, wherein programs are executed on each electrical fuse element by sequentially providing program data to each switching element, in synchronization with a program clock signal.
2. Description of the Related Art
Electrical fuse devices are widely used for integrated circuits (LSIs) including program devices for high frequency trimming. An electrical fuse device comprises electrical fuse elements made of materials such as poly-silicon. An electrical fuse element is serially connected to a bipolar transistor, in which a process, such as “blowing” and “silicidization”, is carried out by allowing a relatively large electrical current of about 1 ampere to flow through the bipolar transistor. Such a process, carried out on electrical fuses, is hereinafter denoted as “the electrical fuse element program” and the act of carrying out such processes is hereinafter denoted as “execution of the program” or “executing (to execute) the program”.
Recently, in the field of semiconductor integrated circuits, a process of depositing silicidized metallic materials onto polysilicon has been developed as a way to form gate materials, in order to reduce electrical resistivities of the gate materials. There has also been developed a technology for electrical fuse elements, which exploits the mechanism of increasing electrical resistivities by blowing the top surface silicide layer with an electrical current flowing through the gate materials, formed in the manner described above, of semiconductor integrated circuits. In the 130 nm and 90 nm process generations of semiconductor integrated circuits, instantaneous electrical current required for executing the program on a fuse element by electrical conduction, is in the range of 10 to 30 milliamperes for each fuse element.
FIG. 17 shows a circuit diagram of an electrical fuse device conventionally used for semiconductor integrated circuits. In FIG. 17, the reference symbol F denotes an electrical fuse element, the reference symbol Q denotes a switching element comprising a PMOS transistor, serially connected to the electrical fuse element F, and the reference numeral 61 is a NAND gate of which output is connected to the gate of the switching element Q.
For a selected electrical fuse element F, in case that the NAND gate 61 is set to a conducting state by an input of a program signal to the NAND gate 61, the conducting NAND gate 61 turns on the switching element Q, allowing electrical current to flow through the electrical fuse element F. The electrical fuse element F is in the form of a micropattern comprising silicides, polysilicon, or metals, and is programmed to be blown, or to increase its electrical resistivity, when a preset current flows through. An electrical fuse element F, in the above configuration, enables recognition of 0/1 signal states, through reading of resistivity of the initial state when the program is not executed and its high resistivity of the state after the program is executed. (Refer, for example, to National Publication of International Paten Application (kohhyou) Hei 11-512879) In the electrical fuse device, a program clock signal is input externally to the shift registers connected to a plurality of fuse cores, and the switching elements, which are serially connected, bring the fuse elements into conduction sequentially, based on the program signal and program data provided by the shift registers.
In conventional configurations, however, when pulses, under the influence of noise, surge or the like, are generated on a program clock terminal, which is devised to input a program clock signal, the fuse element program may possibly be executed, in an unexpected manner, during a program non-execution mode. Once the fuse element program is executed, the electrical fuse element is electrically (physically) blown due to conduction, making the electrical fuse element unrepairable, and the damage becomes fatal.